BANDA ACEH, Indonesia — People gathered in prayer and visited mass graves in Indonesia’s Aceh province on Thursday to mark 20 years since the massive Indian Ocean tsunami hit the region in one of modern history’s worst natural disasters. Many wept as they placed flowers at a mass grave in Ulee Lheue village, where more than 14,000 unidentified tsunami victims are buried. It is one of several mass graves in Banda Aceh, the capital of Indonesia’s northernmost province, which was one of the areas worst hit by a magnitude 9.1 earthquake and the massive tsunami it triggered. People look at